Air conveyors utilize air discharge pressurized air from a flow duct. The air is directed against a container, such as a newly manufactured plastic bottle, to move the bottle along a path. The bottle itself is typically suspended between a pair of guides that support a neck ring formed on the bottle. The guides locate the top of the bottle inside a “U”-shaped channel. The legs of the channel include openings that discharge air directed against the bottle tops. The guides enable the bottles being pushed by the airflow to slide along the guides and move along a conveyor path.
A fan or blower supplying pressurized air to the conveyor duct controls the speed at which the bottles move along the guides. A variable-frequency drive acting on the blower motor controls the pressure and velocity of the air supplied from the blower (the motor is typically a 3 HP electric motor). Increasing motor speed increases conveyor speed, and decreasing motor speed decreases conveyor speed.
At times it is desirable to stop the movement of bottles along the conveyor path. Bottles upstream of the stopped bottles, however, may continue moving and impact against the stopped bottles, denting or otherwise permanently deforming the bottles. Such deformed bottles may be visually unacceptable and may affect downstream process and filling operations. Furthermore, severe damage may even “lock” the bottle to the guide rails and prevent upstream bottles from resuming movement until the locked bottle is removed.
To reduce impact damage, conveyor airflow is limited to reduce bottle speed and match bottle speed with the physical characteristics and material properties of the bottle. Some bottles however, such as paper-thin water bottles or high-density containers having little intrinsic strength, are prone to denting using conventional air conveyors.
Trenel et al. Patent Application Publication 20020192038 discloses an air conveyor in which the conveyor air duct is divided by a wall into upper and lower duct compartments. The upper duct compartment receives pressurized air from the blower. The lower duct compartment provides the pressurized air to the channel for discharge against the bottles.
An opening in the wall near an end of the duct fluidly communicates the upper duct compartment with the lower duct compartment. A flat plate acts as a valving member that opens and closed the opening. When the opening is closed, the lower duct compartment is isolated from the upper duct compartment, stopping the flow of air through the channel and stopping the flow of bottles.
Use of a plate to close an opening near an end of the duct does not allow fine control of air flow. The plate when away from the opening itself acts to subdivide the upper duct compartment, with the result that the plate may impart unwanted turbulence to the airflow. Being near an end of the duct, the control of airflow at the other end of the duct is not optimum.
Rediess et al. U.S. Pat. No. 6,190,094 discloses an air conveyor in which a cap can be selectively raised or lowered over the channel to provide high-speed or low-speed airflow. When the cap is raised, airflow into the channel is unobstructed and the air discharges from the channel at relatively high speed. When the cap is lowered, the cap partially obstructs the channel openings, reducing airflow to relatively low-speed airflow.
Modifying the Rediess et al. air conveyor to shut off airflow is expensive since the cap would need to fit closely over the channel. Using different channels for different bottles or containers would require changing caps, adding additional expense.
Thus there is a need for an air conveyor that can better regulate airflow for controlling the speed of articles being conveyed by the air conveyer.